1. Field of the Invention
The present invention relates to a method of removing a semiconductor film or a metal film by irradiating the same with an energy beam. The present method is applicable to a method of fabricating a photovoltaic element.
2. Description of the Background Art
In a method of fabricating a semiconductor device such as a photovoltaic element, an energy beam such as a laser beam is partially applied to a semiconductor film for removing a fine region thereof. In such a film removal process, the semiconductor film is irradiated with an energy beam having an energy density exceeding the binding energy of the components forming the semiconductor film. It is possible to remove the semiconductor film in a prescribed pattern by scanning the film with a spot-type energy beam or a linear energy beam.
In the semiconductor device such as a photovoltaic element, the semiconductor film may be formed on a metal film. When such a semiconductor film is irradiated with an energy beam such as a laser beam for removing the film, the following problem arises. There are threshold values with respect to energy density in relation to film removal using an energy beam, and the semiconductor film has a higher threshold value than the metal film. Thus, when the semiconductor film that has been formed on the metal film is irradiated with an energy beam having an energy density lower than the threshold value of the semiconductor film, the semiconductor film cannot be removed. On the other hand, when the semiconductor film is irradiated with an energy beam having an energy density higher than its threshold value, the semiconductor film will be removed but the metal film serving as an underlayer will also inevitably be removed at the same time.
In a step of fabricating a semiconductor device such as a photo-voltaic element, an energy beam such as a laser beam is partially applied to a metal film, i.e. applied to a portion of the metal film, for removing a fine region thereof. In such film removal by irradiation with an energy beam, it is possible to remove the metal film in a prescribed pattern by scanning the film with a spot-type energy beam or a linear energy beam.
FIGS. 14A and 14B are sectional views showing a conventional method of removing a metal film. Referring to FIG. 14A, a polymer thin film 10 of polyimide resin or the like is formed on a substrate 1 of glass or the like, and a metal film 2 of Al or the like is formed on the polymer thin film 10. Such a layered structure of the metal film 2 is employed in a photovoltaic element, for example. A laser beam 9 emitted from an XeCl excimer laser, for example, is employed as an energy beam for removing the metal film 2. The metal film 2 is irradiated with the laser beam 9, and is thereby partially removed.
Referring to FIG. 14B, the metal film 2 has been irradiated with the laser beam 9, which has formed a removed portion 2b. While forming the removed portion 2b, a deformed portion such as a projection 2a is formed on a peripheral region of the removed portion of the metal film 2, due to thermal deformation or the like. Such a projection 2a leads to the separation of a semiconductor thin film or the like that is to be stacked on the metal film 2, or to the formation of pinholes and electric leakage and the like in the semiconductor thin film.